Our research is directed toward an understanding of the molecular details of the process of viral RNA synthesis (transcription) and its control in cells infected by oncogenic DNA viruses, such as SV40, polyoma, and adenovirus 2. We have devised an extraction procedure which separates two forms of SV40 transcription complex present in cells at a late stage of infection: a Triton soluble S55 complex and a cell chromatin-associated complex. The transcription complexes contain viral DNA, active RNA polymerase, and other protein. Utilizing this material, it should prove possible to characterize the template and enzyme(s) involved in viral transcription. The chromatin-like complexes will also be used in studies concerning the processing of viral RNA as well as biochemical aspects of the process of RNA synthesis, such as RNA chain termination, release, and reinitiation. This in vitro approach provides an accurate means for examining physiological variations which might influence the rate of viral RNA synthesis in vivo, as assayed by the amount of RNA polymerase per unit of viral DNA. This system also offers the advantage of permitting the study of the effect of purified macromolecules on the process of viral transcription. BIBLIOGRAPHIC REFERENCE: M.H. Green and T.L. Brooks, In: In Vitro Transcription and Translation of Viral Genomes, A.-L. Haenni and G. Beaud, eds. (Paris: INSERM), 33-41 (1975). C.J. Chesterton, B.E.H. Coupar, P.H.W. Butterworth, J. Buss, and M.H. Green, Eur. J. Biochem. 57, 79-83 (1975).